The goals of this program is to identify and explore the mechanisms by which developmental signaling is regulated. The five component projects focus on one class of secreted molecules the TGF-beta-related bone morphogenetic proteins (BMPs) that play important roles in patterning both vertebrate and invertebrate embryos. Currently, there is a basic understanding of how BMPs, and their invertebrate homologues such as Drosophila decapentaplegic (dpp), interact with cellular receptors to produce a signal in the form of a phosphorylated cytosolic Smad protein that translocates to the cell nucleus and influences patterns of gene expression. How levels of BMP activity are controlled-spatially and temporally is much less well understood. Evidence exists of control mechanisms involving activation of gene expression; secreted BMP inhibitors; proteases that cleave BMP-inhibitors; proteins that interact with inhibitor-cleaving proteases; differential expression of receptor isoforms; expression of co-receptors; and the use of multiple Smads. Project I will investigate how the function of chordin, a BMP inhibitor whose levels control BMP function in the early Xenopus embryo, is regulated by the protease BMP-1 and other molecules. Project II will investigate the mechanism by which two BMPs in Drosophila, dpp and screw (scw) interact synergistically. Project III will investigate the mechanism of action of a potentially novel GPI-anchored cell surface protein that acts as a positive regulator of BMP-receptor binding in mammalian cells, as well as investigate the biological significance of BMP binding to heparan sulfate. Project IV will investigate why low doses of some BMPs promote the production of neurons in the mouse olfactory epithelium, while high doses inhibit neurogenesis; this project will focus bone on the mechanism of dose-dependent effects and on identifying the relevant BMPs and BMP actions in vivo. Project V will focus on the molecule twisted gastrulation (tsg), which is required for a dpp-dependent patterning event, but is structurally related to insulin-like growth factor binding proteins; this project will week to identify the interactions that und4erly the biological activities of tsg. Through collaborative and synergistic interactions among the projects, it is hoped that these studies will lead to a broader understanding of how developmental signaling pathways are regulated. Such pathways control virtually every aspect of cell behavior during development, and interference with these pathways is believed responsible for a large proportion of birth defects.